FIGS. 1 and 2 show the conventional seal-ring type shaft-sealing device for sealing a fluid such as a highly pressurized gas or liquid.
In the figures, the reference numeral (1) designates a rotating shaft; (2) designates a housing having side walls (2a), (2b) through which the rotating shaft (1) passes; (3) designates a seal ring formed by a pair of annular rings; (4) designates an antirotation pin secured to the seal ring (3) to prevent it rotation; (5) designates inlets for a sealing liquid which are provided radially in the outer surface of the seal ring at plural positions in order to seal a highly pressurized fluid, the inlets communicating with a single annular groove (6); (7) designates a gap formed between the seal ring and the rotating shaft (1); (8) designates an antirotation pin support formed in the housing (2); and (9) designates a annular space for feeding the sealing liquid radially which is also formed in the housing (2).
Operation of the conventional device having the structure described above will be explained.
The sealing liquid in the housing (2) passes through the inlets (5) of the seal ring (3) to fill the annular groove (6) and provides a liquid film (not shown in the figures) in the gap (7) formed between the rotating shaft (1) and the seal ring (3) and flows, on the one hand, to the sealed side (shown by the symbol G) and on the other hand, to a low pressure side as atmosphere (shown by the symbol A). The pressure (PS) of the sealing liquid is maintained slightly higher than the pressure PG of the fluid to be sealed (gas or liquid) whereby leakage of the fluid to be sealed to the lower pressure side is prevented. The seal ring (3), during operation, floats by hydrodynamic force, producing the liquid film, by the revolution of the rotating shaft (1) so that the seal ring operates in a non-contacting state, i.e. maintaining a gap (7) between itself and the rotating shaft (1).
In the conventional shaft-sealing device, the inner circumference of the seal ring (3) is manufactured a true circle while the seal ring generally operates eccentrically in relation to the rotating shaft (1) as shown by dotted lines in FIG. 3 whereby heat produced in the liquid film formed in the gap (7) by the revolution of the rotating shaft (1) is not uniformly distributed on the inner surface of the seal ring and the seal ring becomes oval shaped by thermal deformation as shown by the solid line in the figure. The minimum liquid film thickness (F) existed in non-thermal deformation is further reduced to the thickness (H) as shown in FIG. 3. This results in an excessive temperature increase in the inner surface of the seal ring (3) and contact with the rotating shaft (1) thereby having an adverse effect on the vibration of the shaft.